Sealed semiconductor housings



i 1 mi@ IIS, I. i 9 um Oct. 5, 1,965` j H, B. RosENBER AL A 3,210,618

g o so ZV 'l '-11 Z i `nited States Patent O 3,210,618 SEALED SEMICONDUCTOR HOUSINGS Harold B. Rosenberg, New Rochelle, andl Jack Weiner, Flushing, N.Y., assignorsv to Electronic Devices, Inc., New Rochelle, N.Y., a corporation of Delaware Filed June `2, 1961,- Ser. No. 114,507

- 1-Claim. (Cl. 3175-234) "f The present invention relates generally to housings for semiconductive elements, andmore particularly to protectively sealed rectifier units.

Dry contact rectifiers or junction diodes are usually constructed of thin and brittle wafers of germanium or silicon. These semiconductive materials are light-sensitive and are subject to corrosion and change of electrical properties under humid conditions. They are also susceptible to abrasion and mechanical shock. Protective coverin'gs are therefore essential for shielding the fragile wafer both mechanically and chemically in order to maintain the uniformityand stability of theelectrical characteristics of the rectifier. t

Another problem arising in connection with rectifiers of the semiconductor type is with respect to heat developed during use. Excessive heat may impair the operation of the rectifier if it is subjected to heavy loads while at elevated temperatures. It is necessary, therefore, to mount the wafer on a metal having. good thermal conductivity so that the heat developed may be dissipated rapidly and efficiently.

In assembling silicon or germanium wafers, it is also necessary to'solder the base contact member thoroughly and uniformly to a base mount to assure good thermal and electrical contact therebetween. Since the sensitive edge of lthe wafer is usually etched to provide a clean surface free of impurities, it is important when mounting the wafer that no solder be permitted to contaminate the etched surface and thereby short-circuit the device.

While various forms of rectifier housings have heretofo're been known, none of these housings satisfies all of the above-noted conditions requisite to optimum operating efficiency. For example, while Ithere are housings in which the wafer is soldered to a metal mount to provide a heat sink, the arrangement is such as to be susceptible to contamination of the junction surface by the solder. In other cases, where the wafer is suspended within a housing and hermetically sealed therein, heat dissipation is poor and the wafer tends to overheat.

Accordingly, it is the principal object of this invention to provide a protectively housed semiconductor element of improved design which overcomes the drawbacks of prior art devices and acts to maintain the uniformity and stability of the characteristics of the element.

More specifically, it is an object of the invention to provide a packaged rectifier in which the semiconductive wafer is chemically and mechanically shielded and which acts rapidly to dissipate the heat developed in use.

Also an object of the invention is Vto provide a packaged diode of the above-noted type which may be either hermetically'sealed or potted.

Still another object of the invention is to provide a packaged rectifier having superior electrical and mechanical characteristics andwhich may be manufactured at relatively low cost.

Briefly stated, these objects are attained in a housing structure in the form of a metallic cup whose base is provided with a central pedestal serving as a mount for the semiconductor wafer, the diameter of the wafer exceeding that of the pedestal whereby the junctionsurface s maintained free and clear of all contaminants, the cup acting as both a shield and a heat sink and being either hermetically sealed or filled with a potting compound.

ice

ferred embodiment of a packaged diode of the potted type i in accordance with the invention.

k FIG. 2 is a transverse section taken in the plane indicated by lines 2 2 in FIG. l.

FIG. 3 is a longitudinal section of another preferred embodiment of a packaged diode of the hermetically sealed type in accordance with the invention.

FIG. 4 is a twin form of packaged rectifier.

FIG.I 4A is a schematic electrical diagram of the rectifier shown in FIG. 4.

FIG. 5 is a stacked form of packaged rectifier.

FIG. 5A is a schematic diagram of the device shown in FIG. 5.

.Referring now to FIGS. l and 2, there is shown a protectively packaged-diode, generally designated by numeral 10, and constituted by a cylindrical wafer 11 having upper and lower contact electrodes 12 and 13 plated thereon. The invention is of particular value in the packaging of semiconductor devices of the p-n junction type, especially silicon or germanium rectifiers, although the invention is not restricted to this application and may be used with other solid state components.

As is well known, if a body of semiconductive material has adjoining zones of the ntype and p-type, the junction between the two zones acts as a rectifying barrier offering a low resistance to current flow in one direction while presenting a high resistance in the reverse direction.

eterup' to one inch and over. The electrodes 12 and 13, which may 'bein the form of a nickel or silver-plated layer on opposing faces of the wafer, ordinarily each have a thickness of .001 inch. Such wafers are extremely fragile and must be carefully protected.

It is important that the exposed edge of the wafer, which is not necessarily circular, be free of contaminants andethat the wafer be sealed against moisture to prevent the formation of surface leakage paths across the junction which lies between the two end electrodes. In practice, after the nickel electrodes are plated on the opposing faces of the wafer, the nickel is sintered to assure an effective bond to the wafer. The wafers are then etched, with an acid solution, and the clean wafers are then rinsed and dried.

The package for the wafer is constituted by a cylindrical metal cup 14 having a base 15 and a circular pedestal 16 projecting upwardly from the center of the base to provide a mount for the wafer. The interior wall of the cup is indented to form a series of annular grooves 17, 18 and 19. The cup is preferably made of a metal vof high thermal conductivity such as brass plated with silver. The cup and the base thereof is relatively thick-walled to afford an effective heat sink to dissipate heat quickly.

The wafer is mounted on the pedestal by soldering the lower electrode 13 to the head of the pedestal, the solder being uniformly spread thereon to' -form a connecting layer 20. The upper electrode 12 'is soldered to a lead wire 21 which is preferably silver-plated and is sinuously Y is however not grooved, for the cup'in this instance After the wafer is soldered on its pedestal mount and the lead 2l is attached, it vmay be desirable to clean the surfaces, particularly if ux is used in the soldering. This cleaning vmay be accomplished ultrasonically in conjunction-with a solvent such as warm trichloroethy'lene. It may also be desirable after the sensitive surface of the wafer is clean to apply a protectivecoating to repel lmoisture, such as a layer of silanes. For example, Dow Corning silicone varnish 996v or -997 diluted with xylene may be used for this purpose.

Finally, the wafer is potted by an`ins'ulating substance 22 filling the entire cup. Suitable for this 'purpose Vis an epoxy which may be mixed with a powdered alumina filler as well as a black pigment. The potting compound may be applied by means of a wooden stick. It will be noted viding in compact form a `full wave rectifier circuit, as

shown schematically in FIG. 4A and 'may Yalso be used4 for such circuits :1s doublers.

ln FIG. V5, there is shown a stacked arrangement of..

rectiers which maybe potted or hermctically sealedv in a container in the manner described above. In ,this arrangement, the wafers 10 and 10A are connected in `series by soldering the -top electrode of wafer 10 tothe bottom electrode of wafer 10A. `Obviously a 'greater'number of tected-with'in their housing. The unitmayreadily be wired that the potting compound enters the grooves 17, A18 and 19, and thereby is locked into thecup. The grooves also act to extend the leakage path of moisture along the interior wall of the cup to the wafer. A second lead .2fM is welded to the bottom of the cup,thereby 'making con- 2Q 'neetion with the bottom electrode 13 of the semiconductive wafer and completing the diode circuit.

i wafer is somewhat greater than that of the pedestal so that lthe sensitive edge surface vthereof is entirely .clear of the pedestal and is elevated above the'base, thereby isov is protectedagainst light, humidity, heat and mechanical acteristics are uniform-and stable'.

Referring now to FIG. 3, there is shownr another embodiment of the invention in which the wafer 10 is` contained in a metal cup 23 having a central pedestal 24 pro-A viding'amount for the wafer. The interior ofthe cup 1s hermetically sealed `Aagainst moisture. y 1

The mouth of the cup is provided with an annularfshoulinto rectitercii-cuits and need Anot be mounted in any 'specialmanner io'n :a chassis or otherwise.

'r While-therehavefbeen shown what are considered to 'be[preferred:embodiments`of the invention, it will 'be anfestthat'rnany lchanges and modifications ymay be made.,ltherinwitliout departing from the Aessential 4spirit:

'--.of.thejinvention. It---isnintendei therefore, rin the annexed jvfclaim to'v cover all such changes and ymodiiications as yfall *.withinlzthetrue scope of the invention.

; vAipackagedIserniconductive .device comprising a semi- `:flcoridlrlctii/"e:wafer having two electrodes yat opposing faces lating this surface. The arrangement is such that the wafer` -thereof,;'afcylindrical metal cup for housing `said wafer y -and havingfzabaseand a` pedestal thereon, one electrode stresses to provide a rectifier yof high efficiency whose chaff.` y

{ofi-sai'dwaferheing bonded'to said pedestal to elevate said wafer-'above:saidbase,'the diameter of said pedestal Vbeing smallerthan l.that of said wafer :whereby `the edge of said jwaferfisffreo'f said pedestal, the ful-l length of the in {ftd-extend 'themoisture leakage path to said wafer, a lead" 35, t

wall of .saidv cup` being circumferentially corrugated -f wirefc'onnected'.tofthe other electrode of said wafer and ,Kgeittendingfromz*saidcup, and a'potting compound filling circled` by a metal ring 27 which, is soldered into the i nal lead '29 is also inserted inthe 4sleeve and solder `is owed therein to interconnect the wires and to seal the cup. Inzpractice, before the cup is sealed it is evacuated and then filled vwith an inert gas such as nitrogen.v

The twin arrangement shown in FIG. 4 is composed of an integral pair of units each one of which may be similar 4to that of FIG. 1 or 3. The pairing of diodes is effected 'by means of a double cup 30 having la base 31 which izs'common to lboth containers, a pedestal projecting from f opposite surfaces of the baseto support the individual wafers 10 and 10A. This arrangement isuseful in prowl'said cupt der 25 adapted to receive a disc-shaped glass seal 26 en- 1 'mageos y seal 'the .wafer therein.

References'Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS France.

y JrtGALVlNQPrimary Examiner.`

BORG N. WESTBY, JAMES D. KALLAM,

' A Examiners. 

